and eventually rose above the latter. More generally, it appears that before each eruption there were two batches of magma present beneath the volcano which however were very similar owing perhaps to a homogenization process that took place deep in the crust. Before the eruption, the magma is estimated to have been hot. Climate and biology Galán lies in a region of arid climate, with annual precipitation amounting to about . Climate data are known for Salar de Hombre Muerto north of Galán; average temperatures there are in summer and winter, respectively. Precipitation occurs mostly during the summer months. Between elevation, vegetation consists of high altitude steppe dominated by Poaceae (grasses) such as Festuca (fescue) and Stipa (feather grass). At lower altitudes, wetlands have their own vegetation. In sheltered areas birds like ducks and flamingos can be observed. Eruptive history Volcanic activity at Galán occurred in two separate stages, which are separated by an erosional unconformity during which the ignimbrite apron of the Toconquis group was incised by deep valleys. Mechanistically, the onset of the eruptions has been explained with delamination events during which parts of the lower crust broke off, asthenospheric material replaced the crust lost by delamination and basaltic magmas penetrated the remaining crust. These stages have left an ignimbrite plateau that surrounds the caldera except on its southern side, and which is noticeable on satellite images. It covers a surface area of about and is the largest ignimbrite system in the Puna plateau. Toconquis Group The first stage occurred between 5.60 and 4.51 million years ago and consisted of the eruption of large ignimbrites such as the Blanco, Cueva Negra, several Merihuaca ignimbrites and Real Grande ignimbrite as well as lava domes, all from north–south trending fractures, forming the Toconquis Group (formerly called the Toconquis Formation). The Real Grande and Cueva Negra ignimbrites were considered to be homologous, as are the easterly Leon Muerto and several Merihuaca ignimbrites, but it was later found that the Leon Muerto and Merihuaca ignimbrites probably were erupted from distinct vent systems and have distinct compositions, and the Cueva Negra ignimbrite was later considered to be a separate formation from the other Toconquis group ignimbrites. The later classifications established a 6.5 5.5 million-year-old Blanco/Merihuaca ignimbrites, 4.8 million-year-old Pitas, 4.7 million-year-old Real Grande, 4.5 million-year-old Vega and 3.8 million-year-old Cueva Negra ignimbrite. The formation is fairly heterogeneous, with some ignimbrites separated by sharp